During aerial refueling operations, a tanker aircraft supplies fuel to a receiver aircraft while in-flight. One approach to aerial refueling is known as probe-and-drogue refueling. In a probe-and-drogue system, the tanker aircraft extends a flexible hose, which trails out behind and below the tanker aircraft. The receiver aircraft has a probe, which the receiver aircraft maneuvers into engagement with a drogue at a free end of the hose of the tanker aircraft. After the probe couples to the drogue and hose, the tanker aircraft supplies fuel to the receiver aircraft provided the receiver aircraft remains within a refueling range of the tanker aircraft.
During an aerial refueling operation, the receiver aircraft is generally responsible for maneuvering relative to the tanker aircraft to couple the probe on the receiver aircraft with the hose and drogue of the tanker aircraft. Once coupled, the receiver aircraft attempts to maintain a position within the refueling range of the tanker aircraft so that the receiver aircraft can receive fuel at a safe distance of separation from the tanker aircraft. To help the receiver aircraft accomplish these tasks, the tanker aircraft may provide to the receiver aircraft positional and/or operational feedback during the aerial refueling operation.
In one approach, the tanker aircraft includes an indication system for providing visual indications of the positional and/or operational feedback to the receiver aircraft. The indication system typically consists of a single not-ready light source for emitting a red light, a single waiting light source for emitting an amber light, and a single refueling light source for emitting a green light to provide indications in the visible light spectrum. Before the receiver aircraft couples to the tanker aircraft, the indication system activates the not-ready light source to indicate that the tanker aircraft is not ready to couple with the receiver aircraft, or the indication system activates the waiting light source to indicate that the tanker aircraft is ready to couple with the receiver aircraft.
After the receiver aircraft couples to the tanker aircraft, the indication system activates the refueling light source to indicate that the receiver aircraft is in the refueling range and receiving fuel from the tanker aircraft. The indication system may flash the waiting light source to indicate that the receiver aircraft exceeded a minimum distance from the tanker aircraft or steadily activate the waiting light source to indicate that the receiver aircraft exceeded a maximum distance from the tanker aircraft (i.e., to indicate that the receiver aircraft is outside of the refueling range). In either scenario, the tanker aircraft immediately ceases supplying fuel to the receiver aircraft until the receiver aircraft maneuvers back into the refueling range. Also, in either scenario, the lights of the indication system provide no advanced warning to the receiver aircraft that it is approaching a boundary of the refueling range and should adjust its position to avoid an immediate shutoff of fuel supply.
To provide additional positional feedback to the receiver aircraft, the tanker aircraft may include markings at various locations on the hose. For example, the hose may include markings to indicate the boundaries of the refueling range. As such, the pilot of the receiver aircraft can determine the position of the receiver aircraft relative to the refueling range by observing a position of the markings relative to a housing of the tanker aircraft from which the hose extends. One drawback is that the pilot may be required to focus on both the hose markings and the lights of the indication system to receive both positional and operational feedback indications. Because the lights and the markings are in different locations, the pilot may repeatedly shift his or her focus between the different locations on the tanker aircraft during the refueling operation. This may present difficulties for the pilot in some instances.
Additionally, the visible light signals emitted by the indication system and the markings on the hose may be challenging for the pilot to observe when operating under low-light conditions such as, for example, during night operations and/or during inclement weather. To address low-light conditions, the tanker aircraft may include a separate set of infrared lights positioned immediately adjacent to the not-ready light source, the waiting light source, and the refueling light source. During low-light conditions, the receiver aircraft can use a night-vision imaging system (e.g., night-vision goggles) to observe when one of the infrared lights is activated. However, because the other infrared lights are not activated, the pilot is required to identify other points of reference on the tanker aircraft to try to determine the relative position of the activated infrared light and ascertain the indication being communicated. Under low-light conditions, it can be challenging to do so because it is often difficult for the pilot to accurately identify points of reference that can be used to determine the relative position of the activated light.